Compact Overlapping Annular Slot Array

A four-element annular slot array is presented for applications requiring omnidirectional gain with minimal variation in azimuthal gain and phase. Cavity-backed annular slots are overlapped to form a single compact array aperture. The slot feed structures are designed to reduce undesirable modes and inter-element coupling. The resulting array achieves a simulated 2.5:1 VSWR bandwidth of 26% with less than +/-1 dB of azimuthal gain pattern ripple at the horizon and less than +/: 20 degrees of horizon azimuthal phase ripple.